An optical see-through glass type display device provides a viewer with a virtual image projected onto the retina thanks to an optical see-through glass. The virtual image is superimposed onto an ambient scene image seen through the glass. The virtual image may be projected by a projector and guided into an eye of the viewer via an optical element on the glass.
When a viewer wears an optical see-through glass type display device, the viewer can observe simultaneously the ambient scene image with some attenuation caused by components of the device and the virtual image projected and guided into the viewer's eye via the projector and the optical element. The relative light power between the ambient scene image and the virtual image on the glass needs to be managed to ensure an adequate contrast of the two images. While the virtual image can be dimmed by adjusting the projector light flux, there is a need of attenuation of the ambient scene image, or even light blocking by some configurations needs to be applied on the ambient scene image to enhance contrast of the virtual image.
US2012068913A1 discloses a see-through head mounted display which includes a lens having an LCD panel as an opacity filter. The LCD panel is used to selectively block portions of a real-world scene so that an augmented reality image to be combined with the real-world scene on the lens appears more distinctly. Even in its transparent state the LCD panel as the opacity filter causes loss of light passing through the LCD panel due to light polarization by the LCD panel, thus any solution to adequately improve the transmission level of the opacity filter is needed.